操作系统创建一个新的进程（子进程），并且在进程表中相应为它建立一个新的表项。新进程和原有进程的可执行程序是同一个程序；上下文和数据，绝大部分就是原进程（父进程）的拷贝，但它们是两个相互独立的进程！此时程序寄存器pc，在父、子进程的上下文中都声称，这个进程目前执行到fork调用即将返回（此时子进程不占有CPU，子进程的pc不是真正保存在寄存器中，而是作为进程上下文保存在进程表中的对应表项内）。问题是怎么返回，在父子进程中就分道扬镳。 -Operating system creates a new process (child process), and the corresponding table in the process as it creates a new entry. New process and the original process is the same executable program　context and data, most of that is the original process (parent process) copies, but they are two independent process! The program should register pc, in the parent, the child process in the context of claim that the implementation of this process is about to return to the fork call (in this case the child does not occupy CPU, the child process is not really saved in the pc register, but as a process context saved in the process table entries in the corresponding.) The problem is how to return the process to split the father and son.